Redundant isinstance checks generated for unions where every member is a model

[AndersBennedsgaard]

When a property is a union of schemas that are all object/model types (e.g. oneOf: [ModelA, ModelB]), the generated to_dict() method checks the type of the value with isinstance before converting it, even though every possible type is converted the exact same way (.to_dict()). The type check doesn't actually change anything, since every generated model class is converted identically.

This makes the generated code harder to read than necessary, and trips up linters (e.g. ruff flags it when using the SIM rules).

Generated today:

if isinstance(self.both_models, Unset):
    both_models = UNSET
elif isinstance(self.both_models, ModelA):
    both_models = self.both_models.to_dict()
else:
    both_models = self.both_models.to_dict()

Expected:

if isinstance(self.both_models, Unset):
    both_models = UNSET
else:
    both_models = self.both_models.to_dict()

Note: This only applies when every member of the union is a model. Unions that mix models with primitives/enums must keep their existing per-member check, since those really do need different handling.

[AndersBennedsgaard]

I submitted a PR at #1487. It's probably easier to look at that to see if it is something we need